The present invention relates to a semiconductor integrated circuit device and particularly relates to a semiconductor integrated circuit device having a power semiconductor element.
An igniter system using a power semiconductor element as an automobile igniter switching semiconductor element is one of purposes of a semiconductor integrated circuit device having a power semiconductor element. FIG. 6 is a circuit diagram showing the configuration of an igniter system according to the background art. As shown in FIG. 6, the igniter system according to the background art includes a one-chip semiconductor device 1, an igniter coil 2, and a battery power supply 3. The one-chip semiconductor device 1 has a power semiconductor element 4, a threshold circuit 5, a pull-down transistor 6, and a resistor 7. Three terminals, that is, an input terminal 8, an output terminal 9 and a ground terminal 10, are provided in the one-chip semiconductor device 1.
Collector and emitter terminals of the power semiconductor element 4 are connected to the output terminal 9 and the ground terminal 10 respectively. The output terminal 9 is connected to the battery power supply 3 through the igniter coil 2. The ground terminal 10 is grounded. A gate terminal of the power semiconductor element 4 is connected to the input terminal 8 through the resistor 7. A gate signal from the outside is input into the input terminal 8.
The threshold circuit 5 generates a reference voltage in its inside. The threshold circuit 5 compares the voltage of the gate signal with the reference voltage. The threshold circuit 5 outputs an on-signal when the voltage of the gate signal is lower than the reference voltage. The threshold circuit 5 outputs an off-signal when the voltage of the gate signal is not lower than the reference voltage. The voltage of the gate signal is supplied as a power supply voltage to the threshold circuit 5.
The pull-down transistor 6 is connected between the gate terminal of the power semiconductor element 4 and the ground terminal 10. The pull-down transistor 6 is turned on when the output signal of the threshold circuit 5 is an on-signal. As a result, the gate terminal of the power semiconductor element 4 is grounded and the gate voltage is provided as a ground voltage so that the power semiconductor element 4 is turned off. On the other hand, the pull-down transistor 6 is turned off when the output signal of the threshold circuit 5 is an off-signal. As a result, the gate signal is transmitted to the gate terminal of the power semiconductor element 4. When the voltage of the gate signal exceeds a threshold voltage of the power semiconductor element 4, the power semiconductor element 4 is turned on.
FIG. 7 is a timing chart showing the gate signal, the output signal of the threshold circuit, the gate voltage of the power semiconductor element and the output current of the power semiconductor element in the igniter system shown in FIG. 6. As shown in FIG. 7, the voltage (a) of the gate signal begins to increase at time T0, reaches the threshold voltage of the power semiconductor element at time T1, reaches the threshold voltage of the pull-down transistor at time T2 and reaches the reference voltage at time T3. Incidentally, assume T0<T1<T2<T3.
During a time period T0-T3, the voltage (b) of the output signal of the threshold circuit increases as the voltage (a) of the gate signal increases. On this occasion, the voltage (b) of the output signal of the threshold circuit is equalized to the voltage (a) of the gate signal because the threshold circuit uses the voltage (a) of the gate signal as a power supply voltage. In this time period, the pull-down transistor is on because the threshold circuit outputs an on-signal. Accordingly, the gate voltage of the power semiconductor element is provided as a ground voltage and the power semiconductor element is turned off, so that the output current is shut off. After the time T3, the threshold circuit outputs an off-signal so that the pull-down transistor is turned off. Accordingly, the voltage of the gate signal is applied to the gate terminal of the power semiconductor element to turn on the power semiconductor element, so that the output current flows.
On the other hand, the following in-vehicle igniter has been heretofore proposed. The in-vehicle igniter includes: an insulated gate semiconductor element which has a collector terminal, an emitter terminal, and a gate terminal; a current control circuit which limits the current flowing in the insulated gate semiconductor element by controlling the voltage of the gate terminal when the current exceeds a predetermined value; a voltage monitoring circuit which detects the electric potential of the collector; and a control current regulating circuit which controls the current flowing in the gate terminal in response to the output of the voltage monitoring circuit (e.g. see Japanese Patent No. 4052815).
Moreover, a configuration in which a control circuit for controlling a signal input to a gate terminal of a power semiconductor element is driven by a battery voltage has been heretofore known commonly (e.g. see U.S. Pat. No. 7,205,822). In addition, a depression type MOS (Metal Oxide Semiconductor) semiconductor element has been heretofore known commonly (e.g. see Japanese Patent No. 2982785.
In the background-art igniter system shown in FIG. 6, there is however the following problem. As shown in FIG. 7, in the time period T0-T2, the voltage (a) of the gate signal, that is, the voltage (b) of the output signal of the threshold circuit is lower than the threshold voltage of the pull-down transistor. Accordingly, in this time period, the pull-down transistor is turned off, so that the voltage of the gate signal is applied as a gate voltage (c) to the gate terminal of the power semiconductor element. After the gate voltage (c) of the power semiconductor element reaches the threshold of the power semiconductor element at time T1, the power semiconductor element is temporarily turned on until the pull-down transistor is turned on at time T2. For this reason, a minute current flows in the power semiconductor element during a time period T1-T2 though it is essentially necessary to shut off the output current (d) of the power semiconductor element during a time period T0-T3.
The area of the power semiconductor element is generally larger than the area of the pull-down transistor. For this reason, there is a possibility that a considerable sub-threshold current may flow if the gate voltage of the power semiconductor element cannot be sufficiently pulled down to the ground voltage even when the threshold voltage of the power semiconductor element is higher than the threshold voltage of the pull-down transistor.
In view of the above, it would be desirable to provide a semiconductor integrated circuit device which can operate a pull-down semiconductor element surely to turn off a power semiconductor element in order to solve the aforementioned problem in the background art.